Dietary L-carnitine Stimulates Carnitine Acyltransferases in the Liver of Aged RatsHeidrun Karlica, Sandra Lohningera,b,c, Thomas Koeckb, and Alfred Lohningerba Ludwig Boltzmann Institute for Leukemia Research and Hematology, Vienna, Austria b Department of Medical Chemistry, University of Vienna, Vienna, Austria c Veterinary University of Vienna, Vienna, Austria Correspondence to: Alfred Lohninger, Dept. of Medical Chemistry, Währinger Str. 10, A-1090 Vienna, Austria. E-mail: alfred.lohninger@univie.ac.at Aging affects oxidative metabolism in liver and other tissues. Carnitine acyltransferases are key enzymes of this process in mitochondria. As previously shown, the rate of transcription and activity of carnitine palmitoyltransferase CPT1 are also related to carnitine levels. In this study we compared the effect of dietary L-carnitine (100 mg L-carnitine/kg body weight/day over 3 months) on liver enzymes of aged rats (months 2124) to adult animals (months 69) and age-related controls for both groups. The transcription rate of CPT1, CPT2, and carnitine acetyltransferase (CRAT) was determined by quantitative reverse transcription real-time PCR (RTQPCR) and compared to the activity of the CPT1A enzyme. The results showed that the transcription rates of CPT1, CPT2, and CRAT were similar in aged and adult control animals. Carnitine-fed old rats had a significant (p<0.05) 812-fold higher mean transcription rate of CPT1 and CRAT compared to aged controls, adult carnitine-fed animals, and adult controls, whereas the transcription rate of CPT2 was stimulated 23-fold in carnitine-fed animals of both age groups. With regard to the enzymatic activity of CPT1 there was a 1.5-fold increase in the old carnitine group compared to all other groups. RNA in situ hybridization also indicated an enhanced expression of CPT1A in hepatocytes from L-carnitine-supplemented animals. These results suggest that L-carnitine stimulates transcription of CPT1, CPT2, and CRAT as well as the enzyme activity of CPT1 in the livers of aged rats. (J Histochem Cytochem 50:205212, 2002) Key Words: carnitine palmitoyltransferases, (CPT1 and CPT2), carnitine acetyltransferase, (CRAT), transcription rate, enzyme activity, rat liver
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